What Makes a Good 4X Game?

I doubt we will ever see a eSport league for a 4X game as they are not the most exciting genre of games that you can play. There's still some great fun to be had for the strategists among us but what is it that make a 4X game great?

• Accessible - 4x games are not easily accessible as they include tons of mechanics. It's important for those game to offer some hand holding especially in the beginning.
• Clear Menu - Reading is a big part of what you need to do in 4x games so having clear menus is a definite requirement and can easily make or break a game.
• Unpredictability - Random events and randomly generated maps are a great way to keep someone invested in a 4X game.
• Not Too Many Turns - A 4X game that requires too many turns for something to happen is no fun. The game must find the right balance.
• Economy - How much of the resource do you need to build something? How do you get more of those resources?
• AI - The A.I. must be setup in a way that it takes full advantage of the tools available to it. The player shouldn't feel like he's driving the communication with them.

Civilization series is on top of my list as far as 4x games goes but the endless series is also rising through this list. What is your favorite 4x game?